1. Field of the Invention
The invention relates to a switch, more particularly to a switch for a variable-speed induction motor.
2. Description of the Related Art
Referring to FIG. 1, a conventional switch 1 for a variable-speed induction motor of a ceiling fan is shown to comprise a lower housing part 10, four conductive connecting pieces 11, a stop block 12, a rotary member 13, a stop disc 14, a driving unit, and a pair of rivets 150 for holding together the aforesaid components. The driving unit includes an upper cover part 15, and a biasing member 16, a beaded chain 17, a transmitting plate 18 and a transmitting axle 19 received in the upper cover part 15.
The lower housing part 10 has a top side formed with four angularly spaced apart retaining grooves 101, 102, 103, 104. Since the retaining groove 101 is deeper than the retaining grooves 102, 103, 104, when the connecting pieces 11 are mounted in the retaining grooves 101, 102, 103, 104, one of the connecting pieces 11 is disposed at a lower level with respect to the other connecting pieces 11.
The stop block 12 is disposed in the retaining groove 101, and is stacked on top of the connecting piece 11 in the retaining groove 101.
The rotary member 13 includes an axle 131 made of an insulator material and formed with a polygonal axle hole 1311, and a conductive member 132 that is sleeved on the axle 131 and that includes a ring portion 1321 and a tongue portion 1322 extending upwardly from the ring portion 1321.
The stop disc 14 is formed with a central hole 141, and is disposed on top of the rotary member 13, the lower housing part 10 and the connecting pieces 11.
The transmitting axle 19 includes a disc portion l91, a cylindrical axle portion 192 extending from a top surface of the disc portion 191, and a polygonal axle portion 193 extending from a bottom surface of the disc portion 191. The polygonal axle portion 193 extends through the central hole 141 in the stop disc 14, and engages fittingly the axle hole 1311 in the axle 131 of the rotary member 13.
The transmitting plate 18 is biased by the biasing member 16 to engage the disc portion 191 of the transmitting axle 19.
The beaded chain 17 has one end connected to the transmitting plate 18, and an opposite end extending outwardly of the upper cover part 15. By operating the beaded chain 17, the transmitting plate 18 can be driven to rotate so as to synchronously drive the transmitting axle 19 and the rotary member 13. Each pulling action of the beaded chain 17 results in 90-degree rotation of the rotary member 13. In other words, four consecutive pulling operations are required to rotate the rotary member 13 back to an initial position. When the rotary member 13 rotates for the first time, as shown in FIG. 2A, the switch 1 configures the induction motor of the ceiling fan for high-speed rotation. When the rotary member 13 rotates for the second time, as shown in FIG. 2B, the switch 1 configures the induction motor of the ceiling fan for medium-speed rotation. When the rotary member 13 rotates for the third time, as shown in FIG. 2C, the switch 1 configures the induction motor of the ceiling fan for low-speed rotation. Finally, when the rotary member 13 rotates for the fourth time, the switch 1 is back to its initial position, in which the induction motor of the ceiling fan is deactivated.
The conventional switch 1 has a drawback in that it is limited for application to a variable-speed induction motor having the tapped starting winding configuration illustrated in FIGS. 2A to 2C. As described in U.S. Pat. No. 6,414,412, the tapped starting winding configuration of FIGS. 2A to 2C is disadvantageous in that stability and balance are adversely affected, and vibration and noise are generated during medium-speed and low-speed operations of the variable-speed induction motor. There is thus a need for a switch that can be easily configured for use with different types of variable-speed induction motors.